Kepler Telescope Results Show Earth May Be Common in the Universe

Though our solar system only has one Earth, there may be billions of planets like it dotted throughout the universe, according to a new analysis of data from NASA’s Kepler Space Telescope.

About one in five stars similar to our sun may have an Earth-size planet orbiting it at a distance that would allow liquid water to exist on the planet’s surface — an area known as the star’s “habitable zone” — according to research presented today at a NASA press conference announcing the results. “We’re finding just with Kepler that planets seem to be the rule rather than the exception,” Eric Petigura, a doctoral researcher at the University of California, Berkeley, said during the conference.

NASA’s Kepler Space Telescope ended its official mission in August 2013 after two of its gyroscopic wheels malfunctioned, leaving scientists unable to point it precisely enough to continue its planet-hunting days. Astronomers are still sorting through the data Kepler collected since its 2009 launch and today announced new results based on the first three years of data.

Just like the moon blocks the sun’s rays during an eclipse, a planet passing between its star and Kepler will produce a change in the star’s brightness. Astronomers looking through the data can find these dimmings and determine a planet’s size and orbital period. But sometimes a planet is missed, either because it never crosses its star or because the brightness of the star fluctuates naturally.

Petigura developed software to correct for these potential errors in planet census data from the 40,000 stars Kepler examined. The researchers found that about 22 percent of sun-like stars, or one in five, should have a planet between one and two times the size of Earth orbiting the star in its habitable zone.

“The main question I think we’ve all asked at some point is how common is this ball of rock that we’re sitting on right now in the universe, and how rare or frequent is life in the universe,” Petigura said. “I think the results coming out of Kepler are an important milestone to answering those questions.”

Astronomers have added 833 new planet candidates to the list since NASA’s most recent update in January 2013, bringing the total to 3,538, 10 of which are less than twice the size of Earth and orbit in their stars’ habitable zones. Future missions, like the infrared James Webb Space Telescope, will seek to learn more about the planets, particularly their atmospheres, to determine whether any have the elements necessary for life.

The Kepler researchers are working on a proposal to use the telescope for other scientific purposes; they expect to submit their proposal this spring. They also still have more data to analyze, which should contain the smallest — and hardest-to-find — planets, according to William Borucki, Kepler’s principal science investigator. “We still have a lot more to discover,” Borucki said. “We have a full year of data that hasn’t been fully analyzed. It’s the most valuable year.”